According to the article "Prototype Satellites Demonstrate In-Orbit Refueling" ( www.space.com/missionlaunches/070404_or ... eling.html ) the two prototype-satellites ASTRO and NextSat in transferring fuel from ASTRO to NextSat - which in principle is the first and major step of refueling.

The same article mentions that the two satellites are part of an Air Force-mission and -project.

I remember well that there is a Centennial Challenges by NASA for orbital depots for fuel etc. These depots would need technologies like those tested by ASTRO and NextSat.

I am not sure at this moment if the Centennial Challenge about depots really has been started - but if not it looks as if it might not been needed any longer. A team of private companies already is working on it - funded by the Air Force.

So it seems that the Air Force is doing what NASA should be interested in and do themselves - and on the other hand it seems to be an example of suboptimal coordination and cooperation.

In reality, its just the Air Force doing what they did before NASA came along. They used to be the main US authority on aero and astronautics. I'm sure they're enjoying the opportunity to get back into it, I know I would.

in my eyes there is the difference that Salyut, MIR and ISS are manned and the refuelling is controlled or supervised by astronauts while the tests done didn't involve no humans.

The main reason to start a talk about it was that I remember issues at this board that this refuelling is risky or so and that in-flight refuelling of airplanes is viewed to be risky also.

In-space refuelling could reduce the costs of flights to the Moon or to other planets and there is significant interest in it because it could prolong the lifetime of satellites.

In between there is another project DARPA does which usually or normally would have been viewed as NASA's task - the technology-project for keeping satellites in their proper orbits using heat got by the sun reported by the article "DARPA Readies Demonstration of Radically New In-Space Propulsion" ( www.space.com/businesstechnology/071029 ... darpa.html ).

It seems that DARPA at least might be a proper partner of NASA - there may be unused synergies.

The supervising and controlling is pratically completely done by the ground control team.

Actually the first Salyut stations equipped with a refueling system had often to do the refueling when the cosmonauts were sleeping because the pumps drew a lot of power and the solar arrays didn't provide much energy, so this could only be done when the most power was available for the pumps.

This was during sleep periods, when life support system were switched to minimum levels and no manual experiments were done.

Talking about lifetime of satellites. One should never forget one of the main problems. The degradation of the solar arrays (paired with practical problems like new technologies not available when the sat was launched, for example imaging equipment).

_________________"The hardest hurdle to space isn't the technicalities and money. But rather, the courage and the will to do it." - Burt Rutan.